An aluminum-based alloy bearing of the type described above ordinarily has a structure comprising a tin containing aluminum-based alloy pressure-welded to a backing steel plate. In order to increase the welding strength between the tin-containing aluminum-based alloy and the backing steel plate, it is indispensable to anneal the welded assembly after pressure welding, and this annealing operation is ordinarily carried out for a long time at a temperature lower than the temperature forming an Al-Fe intermetallic compound. However, if the tin-containing aluminum alloy is exposed to such high temperatures at the above annealing step, aluminum crystal grains and tin precipitates are coarsened in the alloy structure, resulting in reduction of the high temperature hardness and fatigue-resistant strength, which are required for a bearing alloy. In order to eliminate the above defects of the tin-containing aluminum alloy, there has been used a bearing aluminum alloy comprising an additive element incorporated in addition to tin. For example, a tin-containing aluminum alloy comprising 3.5 to 4.5% of Sn, 3.5 to 4.5% of Si, and 0.7 to 1.3% of Cu with the balance being Al, a tin-containing aluminum alloy comprising 4 to 8% of Sn, 1 to 2% of Si, 0.1 to 2% of Cu and 0.1 to 1% of ni with the balance being Al, a tin-containing aluminum alloy comprising 3 to 40% of Sn, 0.1 to 5% of Pb, 0.2 to 2% of Cu, 0.1 to 3% of Sb, 0.2 to 3% of Si and 0.01 to 1% of Ti with the balance being Al, a tin-containing aluminum alloy comprising 15 to 30% of Sn and 0.5 to 2% of Cu with the balance being Al, and a tin-containing aluminum alloy comprising 1 to 23% of Sn, 1.5 to 9% of Pb, 0.3 to 3% of Cu and 1 to 8% of Si with the balance being Al (hereinafter referred to as "multi-component system bearing alloys") have been used for vehicles and the like.
Recently, reduction of the size and increase of the output are required in internal combustion engines for automobiles, and furthermore, attachment of an apparatus for reducing a blow-bye gas is required for purging an exhaust gas. Therefore, conditions under which bearings are used become severe. More specifically, the size of bearings has recently been reduced and the bearings are used under higher load and higher temperature conditions than in the past. Accordingly, fatigue fracture and abnormal abrasion readily occur in the conventional multicomponent system bearing alloys and troubles are caused in internal combustion engines for automobiles by these undersirable phenomena. In metal materials, a fatigue phenomenon ordinarily takes place when they are used over a long period of time, but in recent internal combustion engines, fatigue fracture of bearings is sometimes caused even when a high load operation is conducted for a relatively short time. The temperature of a lubricating oil in an internal combustion engine is increased at a high load operation. For example, the temperature of lubricating oil in an oil pan is elevated to 130.degree. to 150.degree. C., and it is therefore presumed that the bearing has a sliding contact with an opposite member, for example, a crank shaft, at a relatively high temperature. In a conventional multicomponent system bearing alloys, the high temperature hardness is drastically reduced by this sliding contact at high temperatures, and melting or migration of the tin phase is caused in the multicomponent system bearing alloys. We believe that the fatigue-resistant strength is reduced in the multicomponent system bearing alloys because of such reduction of the high temperature hardness and melting or migration of the tin phase.
In recent internal combustion engines, in order to reduce the cost of shafts such as crank shafts, customary shafts of forged steel tend to be replaced by ductile cast iron shafts having a low processing cost and the surface roughness of the shafts tends to increase. On the machine-processed surfaces of ductile cast iron shafts, there are left many cavities formed by shaving and removal of graphite particles at the machine processing, and abnormal abrasion is caused on the surfaces of the bearings because of the edges of these cavities, resulting in fatigue fracture. This is an unavoidable defect of the conventional multicomponent system bearing alloys.
With a view to improving properties of tin-containing aluminum alloys by incorporating various additive elements, we proposed a tin-containing aluminum alloy having chromium and copper incorporated therein in Japanese patent application No. 2690/77 and a tin-containing aluminum alloy having chromium, copper and lead and/or indium in Japanese patent application No. 18225/77. Furthermore, we found that when at least one element selected from silicon, manganese, antimony, titanium, nickel, iron, zirconium, molybdenum and cobalt is incorporated in a tin-containing aluminum alloy and is dispersed and precipitated therein, the hardness and abrasion resistance can be improved, and we proposed this improved alloy in Japanese patent application No. 84233/78.